MOSFET assembly and method for determining abnormality of a single MOSFET using the same

Abstract

A circuit and a diagnostic method are disclosed, whereby abnormalities of a plurality of internal FETs constituting a MOSFET disposed between a secondary battery pack and the electric vehicle having the secondary battery pack therein can be individually diagnosed in an electric vehicle. The voltage across each internal MOSFET is measured while each internal MOSFET is individually turned on / off, and compared with a diagnostic table to determine its abnormality.

Description

Technical Field

[0001] The present invention relates to a diagnostic circuit for parallel MOSFETs including a MUX and a diagnostic method using the diagnostic circuit. More specifically, the present invention relates to a circuit capable of diagnosing a fault of a specific MOSFET among a plurality of MOSFETs (these MOSFETs are connected in parallel to each other) configured to supply power to a vehicle using the MUX, and a method for diagnosing a fault of a specific MOSFET among a plurality of MOSFETs connected in parallel to each other using the circuit. Background Art

[0002] With the development of electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (Plug-In HEV), the demand for lithium secondary batteries is expected to continue to grow. Secondary batteries suitable for electric vehicles are generally used in a configuration in which a plurality of secondary battery cells are assembled. A secondary battery pack having a multi-module structure is generally used, in which a plurality of secondary battery cells are connected in series / parallel to each other.

[0003] The secondary battery pack is provided as a device separate from the electric vehicle. A relay for electrically making / breaking the connection is provided between the secondary battery pack and the electric vehicle.

[0004] 12V, 48V or 400V is usually used as the voltage provided by the secondary battery pack to the vehicle. For 400V, mechanical relays are used due to physical limitations. However, for lower voltages, FETs as an electrical solution have been rapidly adopted as an alternative.

[0005] The advantages of mechanical relays are that they can withstand high voltage and high current, can be used at high temperatures, and are cheap. In contrast, noise is generated due to contact with the contacts when turning on / off, and the life of the mechanical relay is limited due to sparks generated when contacting the contacts. In addition, the disadvantage of mechanical relays is that they have low resistance to physical shocks due to their internal mechanical components.

[0006] When a vehicle stops suddenly or a vehicle collision occurs, a very large gravitational acceleration is applied to the vehicle. As a result, the mechanical relay may be damaged. Due to this damage and short circuit, secondary accidents such as fire may occur.

[0007] MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is a representative electrical relay. The disadvantage of MOSFET is that it generates a lot of heat because its capacity and material resistance (RDS) are lower than those of mechanical relays. Depending on the situation, the temperature may rise to 200℃ or more due to resistance.

[0008] Although MOSFETs generate heat and are expensive, they have advantages over mechanical relays in that their life is semi-permanent and they are rarely damaged by physical impact. Therefore, MOSFETs are expected to replace mechanical relays in many vehicles. Since the noise generated by the operation of mechanical relays also needs to be constantly eliminated, it is expected that electrical relays will be used rapidly first in high-priced vehicles.

[0009] As long as the problems related to capacity and heat generation are solved, MOSFET will replace mechanical relays in electric vehicles except high-voltage vehicles. Various types of research have been conducted as follows: Although there are oxidation problems due to moisture and oxygen, in order to prevent contact with the outside air or to increase the heat transfer area, the case is removed from the FET and the FET is directly connected to the metal current collector.

[0010] For MOSFETs currently applied to some vehicles, due to issues such as capacity, multiple MOSFETs are used in a state of being connected in parallel to each other. Multiple MOSFETs are controlled by a single driver. When actually observed from the outside, a single MOSFET seems to be used for a vehicle. However, in many cases, six internal FETs or internal MOSFETs (hereinafter referred to as "internal FETs") having a 2S3P structure (three dual series groups connected in parallel to each other) are provided. Depending on the required capacity, the number of internal FETs can be increased in various ways, for example, to 6, 10, or 12.

[0011] As described above, the internal FETs are connected in series and in parallel with each other. So far, no circuit or method capable of determining abnormality of some of the internal FETs has been proposed.

[0012] In the case where some of the internal FETs are damaged and thus continuously connected to each other (fail-on), the current that does not flow through the internal FETs but flows in a distributed state is concentrated on the damaged internal FETs, so that the damaged internal FETs are easily overheated. As a result, the entire system may overheat. Overheating of the battery pack may be a fatal factor affecting vehicle safety.

[0013] Figure 1 : is a connection circuit diagram of a conventional MOSFET for a vehicle. The power supplied from the vehicle battery pack BAT is controlled by a single MOSFET visible from the outside. Figure 1 In the example, the portion indicated by the single-dot chain line corresponds to a single MOSFET visible from the outside. Figure 1 The internal FETs shown are connected to each other to have a 2S3P structure, but can be changed to various other combinations.

[0014] FET1 to FET6 represent six internal FETs. N-type MOSFETs or P-type MOSFETs can be used as required. In all the drawings of the present invention, only N-type MOSFETs are shown; however, P-type MOSFETs can be easily selected to replace N-type MOSFETs as required.

[0015] When no voltage is applied to the gate, FET1, FET2, FET3 and FET4, FET5, FET6 operate differently. When voltage is applied to the gate, current can flow in the direction from the battery pack to the vehicle ( Figure 1 When no voltage is applied to the gate, the current flows in the direction from the vehicle to the battery pack ( Figure 1 When a voltage is applied to the gate, current can flow through FET4, FET5, and FET6 in the direction from the vehicle to the battery pack, opposite to FET1, FET2, and FET3. When no voltage is applied to the gate, current flows through the diode in the direction from the battery pack to the vehicle.

[0016] In the absence of a voltage applied to the gate, all FETs are inoperative; however, for FET1, FET2, and FET3, current can flow in the reverse direction ( Figure 1 From right to left in the figure) flows through individual diodes or internal parasitic diodes, while for FET4, FET5 and FET6, the current can flow in the forward direction ( Figure 1 That is, for FET1, FET2, and FET3, the current can flow in the direction from V2, V3, and V4 to V1, respectively, and for FET4, FET5, and FET6, the current can flow in the direction from V2, V3, and V4 to V5, respectively.

[0017] Figure 1 All conventional MOSFETs are controlled at once by a single driver. V2, V3, and V4 are Figure 1 The reason for connecting the MOSFETs to each other is that when a large amount of current flows instantaneously due to sudden acceleration or braking of the vehicle, the current needs to be distributed to multiple internal FETs. Conventional MOSFETs for vehicles are turned on / off at the same time by a single driver, and there is no method of diagnosing errors in some of the internal FETs.

[0018] Patent Documents 1 to 3 have in common that they all relate to a technique for diagnosing a failure of a plurality of FETs connected in parallel to each other.

[0019] In the specific configuration, the configuration of patent document 1 is complicated because the voltage value of the resistor is detected separately using the mirror FET set at each FET, and each separate mirror FET needs to be additionally maintained. Patent document 2 is similar to the above patent documents in that the change in the voltage value of the load-side terminal (i.e., the final output) generated by controlling the on / off of multiple FETs is measured to diagnose the fault. However, in patent document 2, a separate power supply for detection is not used, so the current measurement device required for the high voltage must be provided separately. In addition, patent document 2 does not propose a solution such as a specific circuit. The structure of patent document 3 is complicated because: the drive of all FETs is individually controlled, a separate resistor for current detection is added to each FET, and multiple components are added for its maintenance. In addition, the failure of the diagnostic circuit itself may become a problem.

[0020] As described above, an effective method capable of diagnosing abnormality of a single FET of a MOSFET in an electric vehicle having a secondary battery pack has not yet been proposed, and thus the risk of accidents caused by MOSFETs has increased as demand therefor will continue to increase from now on.

[0021] Japanese Patent Application Publication No. 2000-293201 (Patent Document 1)

[0022] Japanese registered patent publication No. 5526965 (Patent document 2)

[0023] Korean Patent Application Publication No. 2016-0041495 (Patent Document 3) Summary of the invention

[0024] Technical issues

[0025] The present invention is made in view of the above problems, and an object of the present invention is to provide a circuit capable of individually diagnosing abnormalities of multiple internal FETs constituting a MOSFET arranged between a secondary battery pack and an electric vehicle having the secondary battery pack therein, and a method of diagnosing abnormalities of the internal FETs using the circuit.

[0026] Another object of the present invention is to provide a circuit and method capable of individually diagnosing abnormalities of both a MOSFET provided on a battery pack side and a MOSFET provided on a vehicle side, among two MOSFETs connected in series with each other.

[0027] Technical Solution

[0028] In order to achieve the above objectives, the present invention provides a MOSFET component, which includes a plurality of MOSFETs, which are configured to control the connection between the positive (+) terminal of a secondary battery pack configured to provide power to a vehicle and a vehicle configured to receive power from the secondary battery pack, and the plurality of MOSFETs are connected in series and in parallel to each other, wherein the MOSFET component includes a MUX having a channel connected to the gate of the MOSFET of the MOSFET component.

[0029] The MOSFET assembly according to the present invention may further include an additional parallel connection component including a switch provided between a positive (+) terminal of the secondary battery pack and a vehicle configured to receive electric power from the secondary battery pack.

[0030] The MOSFET component according to the present invention may further include: a driver module which is an input terminal of the MUX; and a microcontroller unit configured to provide an input corresponding to the total number of channels required to control the MUX.

[0031] The MOSFET component may be configured such that two MOSFETs are connected in series to each other and two or more pairs of two MOSFETs connected in series to each other are connected in parallel to each other.

[0032] Of the two MOSFETs connected in series with each other, the MOSFET arranged on the battery pack side can be operated so that when a voltage is applied to the gate, current flows in a direction from the battery pack to the vehicle, and a diode can be provided, which is configured to allow current to flow through the diode in a direction from the vehicle to the battery pack when no voltage is applied to the gate.

[0033] Of the two MOSFETs connected in series with each other, the MOSFET arranged on the vehicle side can be operated so that current flows in a direction from the vehicle to the battery pack when a voltage is applied to the gate, and a diode can be provided, which is configured to allow current to flow through the diode in a direction from the battery pack to the vehicle when no voltage is applied to the gate.

[0034] The MOSFETs provided on the battery pack side and the vehicle side may be symmetrical to each other.

[0035] The diode may be a separately connected diode or a parasitic diode provided in a MOSFET.

[0036] The MOSFET assembly may be composed of a single MOSFET in appearance, and the MOSFET assembly may be controlled by a battery management system (BMS) of the secondary battery pack.

[0037] In addition, the present invention provides a method for determining an abnormality of a single MOSFET using a MOSFET component, the method comprising the following steps: measuring the voltage across each single MOSFET while sequentially turning on / off the channels of the MUX. The method may also include measuring the voltage across all single MOSFETs. In the method, the MOSFET component may be configured so that two MOSFETs are connected in series with each other and two or more pairs of two MOSFETs connected in series with each other are connected in parallel with each other, and the method may also include the following steps: using the current provided from the battery pack to determine the abnormality of the MOSFET provided on the battery pack side among the two MOSFETs connected in series with each other.

[0038] In addition, the present invention provides a method for determining an abnormality of a single MOSFET using a MOSFET assembly that also includes an additional parallel connection component, the additional parallel connection component including a switch disposed between a positive (+) terminal of a secondary battery pack and a vehicle configured to receive power from the secondary battery pack, the method comprising the following steps: 1) disconnecting the switch; 2) measuring the voltage across each single MOSFET while sequentially connecting / disconnecting only the channel of the MOSFET disposed on the battery pack side among the channels of the MUX; 3) connecting the switch; and 4) measuring the voltage across each single MOSFET while sequentially connecting / disconnecting only the channel of the MOSFET disposed on the vehicle side among the channels of the MUX. The method may also include measuring the voltage across all single MOSFETs in each of steps 2) and 4).

[0039] The method may also include comparing voltage values ​​across all of the MOSFETs with each other to determine abnormality of a single MOSFET.

[0040] The present invention can be provided in a state where any combination of the above inventions is feasible. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a connection circuit diagram of a conventional MOSFET used in vehicles.

[0042] Figure 2 It is a partial modification of the connection circuit diagram of the conventional MOSFET used in vehicles.

[0043] Figure 3 is a connection circuit diagram of a MOSFET for a vehicle according to a first embodiment of the present invention.

[0044] Figure 4 is a connection circuit diagram of a MOSFET for a vehicle according to a second embodiment of the present invention. DETAILED DESCRIPTION

[0045] Now, the preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement the preferred embodiments of the present invention. However, when describing the working principle of the preferred embodiments of the present invention in detail, the detailed description of the known functions and configurations incorporated herein will be omitted when the detailed description may obscure the subject matter of the present invention.

[0046] In addition, the same reference numerals will be used throughout the drawings to refer to components that perform similar functions or operations. Where a component is said to be connected to another component throughout the specification, not only may a component be directly connected to another component, but a component may be indirectly connected to another component through yet another component. In addition, unless otherwise mentioned, including a certain element does not mean excluding other elements, but means that the element may be further included.

[0047] Hereinafter, the present invention will be described in more detail.

[0048] Figure 2 It is a partial modification of the connection circuit diagram of the conventional MOSFET used in vehicles.

[0049] In the present invention, a part of the connection circuit diagram of a conventional MOSFET for a vehicle is changed to determine the abnormality of a single MOSFET. Figure 1 However, in the present invention, V2, V3 and V4 are short-circuited, thereby changing the connection circuit diagram of the MOSFET so that two single MOSFETs are connected in series with each other and multiple pairs of two single MOSFETs are connected in parallel with each other.

[0050] Figure 3 is a connection circuit diagram of a MOSFET for a vehicle according to a first embodiment of the present invention. Figure 4 FIG. 1 is a connection circuit diagram of a MOSFET for a vehicle according to a second embodiment of the present invention. Figure 3 and Figure 4 The present invention is described.

[0051] Including Figures 1 to 4 In the specification of the present application, the term "FET" means a MOSFET used for a power supply.

[0052] The present invention relates to a MOSFET component configured so that a plurality of MOSFETs (FET1 to FET6) are connected in series and in parallel with each other, and the plurality of MOSFETs (FET1 to FET6) are configured to control the connection between the positive (+) terminal of a secondary battery pack configured to supply power to a vehicle and a vehicle configured to receive power from the secondary battery pack. Here, the connection points of the vehicle are represented by V6 and V7.

[0053] FET1 to FET6 represent six internal FETs. They can be N-type MOSFETs or P-type MOSFETs as required. In all the drawings of the present invention, only N-type MOSFETs are shown; however, P-type MOSFETs can be easily selected to replace N-type MOSFETs as required.

[0054] When no voltage is applied to the gate, FET1, FET2, FET3 operate differently from FET4, FET5, FET6. When a voltage is applied to the gate, current can flow through FET1, FET2, and FET3 in the direction from the battery pack to the vehicle. When no voltage is applied to the gate, current flows through the diode in the direction from the vehicle to the battery pack. When a voltage is applied to the gate, current can flow through FET4, FET5, and FET6 in the direction from the vehicle to the battery pack, contrary to FET1, FET2, and FET3. When no voltage is applied to the gate, current flows through the diode in the direction from the battery pack to the vehicle.

[0055] The 6 MUXs connected to the gates of the MOSFETs of the MOSFET components have a total of six channels CH1, CH2, CH3, CH4, CH5, and CH6, and the channels are controlled by control signals S0, S1, S2 transmitted from the microcontroller unit MCU.

[0056] A driving module as an input terminal of the MUX is also connected to the MUX.

[0057] It is possible to further add CH7 to the MUX. In the case where no diagnostics are performed, normal operation can be performed by CH7, which can centrally control all FETs and switches. Figure 3 In this case, FET1, FET2, and FET3 can be continuously turned on through CH7. At this time, the other channels (ie, CH1 to CH6) are turned off.

[0058] In the MOSFET component, two MOSFETs are connected in series to each other, and two or more pairs of two MOSFETs connected in series to each other are connected in parallel to each other.

[0059] A diode configured to allow current to flow in a direction from the vehicle to the battery pack when no voltage is applied to the gate is provided at the MOSFET (FET1, FET2, and FET3) provided on the battery pack side among two MOSFETs connected in series to each other.

[0060] A diode configured to allow current to flow in a direction from the battery pack to the vehicle when no voltage is applied to the gate is provided at the MOSFET (FET4, FET5, and FET6) provided on the vehicle side among two MOSFETs connected in series with each other.

[0061] The diode may be a separately connected diode or a parasitic diode provided in a MOSFET.

[0062] A method of determining an abnormality of a single MOSFET using a MOSFET for a vehicle according to a first embodiment of the present invention includes:

[0063] The step of measuring the voltage across each individual MOSFET while sequentially switching on / off the channels of the MUX.

[0064] The method may further comprise the step of measuring the voltage across all individual MOSFETs.

[0065] When a certain channel is turned on by MUX, the channel is turned on to generate a signal so that the corresponding FET works. When CH1 is turned on, voltage is applied only to the gate of FET1. For example, assuming that the voltage of the battery pack is 48V and FET1 is working normally, when only FET1 is turned on, V1, V2, and V5 are each 48V, and V3 and V4 are each 0V. When FET1 is continuously turned on (faulty conduction or short circuit), even if all FETs are turned off, V1, V2, and V5 are each 48V. When FET1 is continuously turned off (faulty cutoff), even if only FET1 is turned on, only V1 is 48V.

[0066] The diagnostic table for FET1 is shown below.

[0067]

[0068] The above method can be used to determine the abnormality of FET1, FET2, and FET3. For FET2 and FET3, the values ​​corresponding to V2 are replaced by V3 and V4, respectively.

[0069] Compared with the first embodiment, the connection circuit diagram of the MOSFET for a vehicle according to the second embodiment of the present invention further includes an additional parallel connection component including a switch SW1 disposed between the positive (+) terminal of the secondary battery pack and the vehicle, the switch SW1 being configured to receive power from the secondary battery pack. The switch SW1 is connected only for diagnosis.

[0070] A method for determining an abnormality of a single MOSFET using a MOSFET assembly for a vehicle according to a second embodiment of the present invention includes:

[0071] 1) Steps to disconnect the switch;

[0072] 2) while sequentially turning on / off only the channels configured to control the MOSFETs provided on the battery pack side among the MUX channels, measuring the voltages across the respective single MOSFETs;

[0073] 3) Steps of turning on the switch; and

[0074] 4) A step of measuring voltages across respective single MOSFETs while sequentially turning on / off only channels configured to control MOSFETs provided on the vehicle side among channels of the MUX.

[0075] The method may further comprise the step of measuring the voltage across all the individual MOSFETs in each of step 2) and step 4).

[0076] When a certain channel is turned on by MUX, the turned-on channel generates a signal so that the corresponding FET works. When CH1 is turned on, the voltage is applied only to the gate of FET1. For example, assuming that the voltage of the battery pack is 48V and FET1 is working normally, when only FET1 is turned on, V1, V2, and V5 are each 48V and V3 and V4 are each 0V. When FET1 is continuously turned on (faulty conduction or short circuit), even if all FETs are turned off, V1, V2, and V5 are each 48V. When FET1 is continuously turned off (faulty cutoff), even if only FET1 is turned on, only V1 is 48V.

[0077] In the opposite case, when SW is turned on, a voltage of 48V is also applied to V5. When CH4 is turned on, voltage is applied only to the gate of FET4. For example, assuming that the voltage of the battery pack is 48V and FET4 is operating normally, when only FET4 is turned on, V1, V2, and V5 are each 48V, and V3 and V4 are each 0V. When FET4 is continuously turned on (faulty on or short-circuited), even if all FETs are turned off, V1, V2, and V5 are each 48V. When FET4 is continuously turned off (faulty off), even if only FET4 is turned on, only V1 and V5 are each 48V.

[0078] The diagnostic tables for FET1 and FET4 are shown below.

[0079]

[0080] The above method can be used to determine the abnormality of FET1, FET2, FET3, FET4, FET5 and FET6. For FET2 and FET3, and FET5 and FET6, the value corresponding to V2 is replaced by V3 and V4, respectively.

[0081] Figure 3 and Figure 4 Two series connections and three parallel connections are schematically shown. However, in the case where multiple series connections are used instead of two series connections, the solution principle of the present invention is also applicable, and therefore the above structure must also be included in the scope of the rights of the present invention.

[0082] Although the specific details of the present invention have been described in detail, it will be understood by those skilled in the art that the detailed description thereof only discloses the preferred embodiments of the present invention and is therefore not intended to limit the scope of the present invention. Therefore, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope and technical concept of the present invention, and it is apparent that these changes and modifications fall within the scope of the appended claims.

[0083] (Description of Reference Numerals)

[0084] 10: Connection circuit diagram of conventional MOSFET for vehicles

[0085] 20: Partial modification of the connection circuit diagram of the conventional MOSFET for vehicles

[0086] 30: Connection circuit diagram of MOSFET for vehicle according to the first embodiment of the present invention

[0087] 40: Connection circuit diagram of MOSFET for vehicle according to the second embodiment of the present invention

[0088] BAT: Secondary battery pack

[0089] V1, V2, V3, V4, V5, V6, V7: Voltage measurement points

[0090] FET1, FET2, FET3, FET4, FET5, FET6: Internal FET

[0091] MCU: Microcontroller Unit

[0092] CH1, CH2, CH3, CH4, CH5, CH6, CH7: MUX control channels

[0093] S0, S1, S3: Input part sent by the microcontroller unit

[0094] Industrial Applicability

[0095] As is apparent from the above description, the present invention has the advantage that, in an electric vehicle having a secondary battery pack, abnormalities of a plurality of internal FETs constituting a MOSFET disposed between the secondary battery pack and the electric vehicle can be individually diagnosed. Therefore, the present invention can provide an electric power system having higher safety than conventional MOSFET components.

[0096] This application claims priority to Korean Patent Application No. 2019-0150213 filed on November 21, 2019, Korean Patent Application No. 2019-0150214 filed on November 21, 2019, and Korean Patent Application No. 2020-0155900 filed on November 19, 2020, the disclosures of which are incorporated herein by reference in their entirety.

Claims

1. A metal oxide semiconductor field effect transistor MOSFET component, the MOSFET component comprising a plurality of MOSFETs configured to control connection between a positive terminal of a secondary battery pack for supplying power to a vehicle and the vehicle for receiving power from the secondary battery pack, the plurality of MOSFETs being connected in series and in parallel with each other, in, The MOSFET assembly comprises: a MUX having a channel connected to a gate of the MOSFET of the MOSFET component; a driver module, which is an input terminal of the MUX; and a microcontroller unit configured to provide an input corresponding to the total number of channels required to control the MUX, Wherein, when in use, the microcontroller unit is configured to measure the voltage across each individual MOSFET while sequentially switching on / off the channels of the MUX.

2. The MOSFET assembly according to claim 1, further comprising an additional parallel connection component including a switch provided between the positive terminal of the secondary battery pack and the vehicle for receiving power from the secondary battery pack.

3. The MOSFET component according to claim 1 or 2, in, The MOSFET component is configured such that two MOSFETs are connected in series to each other and two or more pairs of the two MOSFETs connected in series to each other are connected in parallel to each other.

4. The MOSFET component according to claim 3, in, The MOSFET provided on the secondary battery pack side of the two MOSFETs connected in series with each other operates so that current flows in a direction from the secondary battery pack to the vehicle when a voltage is applied to a gate, and a diode configured to allow current to flow therethrough in a direction from the vehicle to the secondary battery pack when no voltage is applied to the gate is provided, and The MOSFET arranged on the vehicle side among the two MOSFETs connected in series with each other operates so that when a voltage is applied to the gate, current flows in a direction from the vehicle to the secondary battery pack, and a diode is provided which is configured to allow current to flow through it in a direction from the secondary battery pack to the vehicle when no voltage is applied to the gate.

5. The MOSFET component according to claim 4, in, The diode is a separately connected diode or a parasitic diode provided in the MOSFET.

6. The MOSFET component according to claim 1 or 2, in, The MOSFET component is composed of a single MOSFET.

7. The MOSFET component according to claim 1 or 2, in, The MOSFET component is controlled by a battery management system BMS of the secondary battery pack.

8. A method for determining anomalies of individual metal oxide semiconductor field effect transistors MOSFET using the MOSFET assembly according to claim 1, the method The following steps are involved: While sequentially switching on / off the channels of the MUX, the voltage across each individual MOSFET is measured.

9. A method for determining an abnormality of an individual metal oxide semiconductor field effect transistor MOSFET using the MOSFET assembly according to claim 2, the method The following steps are involved: 1) Disconnect the switch; 2) while sequentially turning on / off only the channels configured to control the MOSFETs provided on the secondary battery pack side among the channels of the MUX, measuring the voltages across the individual MOSFETs; 3) Turn on the switch; as well as 4) While sequentially turning on / off only the channel configured to control the MOSFET provided on the vehicle side among the channels of the MUX, the voltage across each individual MOSFET is measured.

10. The method according to claim 8 or 9, further comprising: The following steps are involved: The voltage values ​​across all MOSFETs are compared with each other to determine abnormality of the individual MOSFETs.

11. The method according to claim 8 or 9, in, The MOSFET component is configured such that two MOSFETs are connected in series with each other and two or more pairs of the two MOSFETs connected in series with each other are connected in parallel with each other, and The method further includes the step of determining an abnormality of a MOSFET provided on a secondary battery pack side among the two MOSFETs connected in series to each other using a current supplied from the secondary battery pack.

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